A blade adjustment is one of the cardinal problems of any type of flow machine affecting equally a structural strength correlated with an operation of the machine at high speeds, safety of a structure and flow losses. A few principal structures of the flow machine are known. Axial machines with radial, non-adjustable blades, for instance, steam turbines, utilize a so-called fur top attachment meeting high operational demands as a result of a form-locking engagement. Hydraulic turbines, for example, Kaplan-type propeller turbine, utilize adjustable blades providing high efficiency and methods for adjusting the blades are known. Generally, blades are attached outside the flow area of medium driving an actual blade. However, design problems often arise when ,under certain circumstances, a blade should be attached within the flow area causing high flow losses.
In machines characterized by the medium flowing transversely to a blade of the machine, so called transverse flow machines, the blade attachment gains particular significance when such a machine is provided with a small number of blades.
The FRENCH patent 604,390 describes the importance of a stream line shape for the blades in a so called Darrius-rotor. Rotor blades in the transverse machines are exposed to a varying load causing a fatigue effect. Due to the high density of liquid, structural strength of the blade attachment gains a critical role for an entire structure. Particularly, designing a structure of the blade attachment, not only the operational speed, but also a run away speed, attained by a turbine upon interrupting of the breaking moment of a generator, should be taken into consideration.
In hydraulic turbines the run away speed is twice as high as the operational speed. Considering the influence of centrifugal forces, the ratio between the run away and operational speed is even larger rendering the run away speed to be approximately four times as high as the operational speed.
This phenomena affects detrimentally the machines with adjustable blades attached to an insert element during an operation by increasing the wear of the blades. As a result, additional structural demands are brought to both a structure of the insert element and sealing connections thereof preventing penetration of pollutants carried by the medium.
The known structures of a pivot element negatively affects the structure as well. As known in the art, a blade length with known blade attachments is to be extended at more than 20% of the blade length. As a consequence, the blade effectiveness is decreased at more that 30%.